Small Engines (Lawn Mowers, etc.): 17.5 HS Briggs shears flywheel key

Question
QUESTION: Eric
few months ago I asked you about issue

http://www.allexperts.com/user.cgi?m=6&catID=1746&expID=17636&qID=5054361

Riding mower Troy Bild 13AD609G063 with Briggs Stratton 311777 type 148-E1 engine 17.5 HP –
I assembled the engine  verifying a good timing (camshaft to valves aligned, etc) and at the start, with engine cranking, it pop and shared the flywheel key. It happened twice., I got the keys from online supplier, original B&S (I think) but looks like soft metal.
What would be the reason for that?

Do i need a "better" key or is there other issue like compression release not working.

I would really appreciate your help on this (before I take this engine apart yet again).

Thank you.

Igor

ANSWER: What are the valve clearances?

Eric

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QUESTION: Eric
They were as per spec - 004” (intake) and .006” exhaust valve.; I do have a pdf manual and I checked that before couple of times.

ANSWER: Did the manual describe how to check the compression release and did it discuss how to properly time the crankshaft and camshaft?

One trick that I have used over the years it to lap the flywheel and crankshaft taper.  Do you have some fine grit lapping compound?

Is there a washer on top of the flywheel retainer cup?

Eric

---------- FOLLOW-UP ----------

QUESTION: I'll have a look at re-lapping as I haven't done that, of course.
There is a washer but I think I didn't torque the bolt enough.

When i assembled the engine I didn't paid attention to compression release, hence my question if that could be the issue.
I made (double ) sure that camshaft/crankshaft gears are aligned as per manual (very good picture) so that is 100% good.

Basically, plan is to open the engine and have a look at compression release mechanisms and make sure flywheel is properly torqued with new key.
does this sound reasonable? what else should I look for?

Thank you.

Answer
It wouldn't hurt to very/check the compression release on the cam.

Make sure to look at the parts diagram and make sure the flywheel washers and bolt are assembled in the correct order.  I forgot to put the washer on once and the engine kept shearing keys.

Eric